The use of microfluidics in the analysis and quantitation of biological and chemical samples is well known. One such use involves a system that utilizes a microfluidic chip (sometimes referred to as a “lab-on-a-chip”) to obtain one or more samples, to process the sample(s) for measurement, and then to assess the composition of the sample using, for example, spectrophotometry or optical tracking of radioactive or fluorescent markers previously placed in the samples. The microfluidic chip typically includes a number of wells into which dyes and reagents are deposited for interaction with the samples. The wells are linked via microchannels to a separation microchannel through which the samples are drawn for analysis. Samples are typically provided as a group on a multi-well sample plate, which are then loaded (or “sipped”) in series onto the chip for combination with reagents and/or dyes and then analysis by the system.
One advantageous application of microfluidics is the electrophoretic analysis of proteins in a biological sample. In this technique, an electrical field is applied to a sample which, in some cases, has been dyed and denatured. The electrical field causes molecules of different types to separate due to the difference with which each type of molecule interacts with the electrical field. For example, different types of proteins have different molecular sizes, so different types of proteins will travel through a material (such as a gel) at different rates depending on their sizes due to the force of the electric field. The proteins, thus separated, can be identified and their attributes measured.
Microfluidic systems are extremely precise measurement tools, and those of skill in the art have occasionally encountered problems with variation in the results of measurements of samples using microfluidics. It has been found that minor fluctuations in the parameters of analysis have a profound effect on the repeatability of the analysis. For example, fluctuations in the features of one microfluidic chip compared to another chip intended to be identical can cause unwanted variation in measurement results. Such fluctuations can include variations in the dimensions of the microchannels. Fluctuations in the attributes of the required reagents can also cause unwanted variations. These can include variations in the dye fluorescence and concentration of the reagents. Similarly, there can also be fluctuations in the test conditions that cause variations in the measured results. These include the power of the laser used to illuminate the sample, the focus position of the laser, and the volume of sample or reagent injected for analysis. Each of the foregoing, and many others not listed, can affect the run-to-run variation in the measurement signal of a microfluidics analysis.
Thus, there is a need in the art to improve the consistency of measured results across multiple runs from a microfluidic system and measurement method. It is further desired that such an improvement be implemented with minimal disruption to currently-employed measurement processes and with minimal cost to the manufacturer and user of the relevant test equipment. Further, it is desired that such improvements be adaptable for use in the context of each of the many possible causes of significant run-to-run variations.